The invention relates to a control system for a purge valve that can be actuated by low pressure, provided for a low-pressure drainage system, enclosing a housing with external wall, a dynamic pressure, caused by waste water accumulated in this, of the first valve that can be switched over to a second position, a first chamber restricted by the first valve that can pressure-adjusted by the first membrane. In doing so, the first membrane is functionally connected with a second valve, via which low pressure or atmospheric pressure is reached as a function of its position at the purge valve, a first connection, through which the first chamber can be connected with a low pressure source, which is blocked in case of missing or too low dynamic pressure by the first valve located in its first position and is released with sufficient dynamic pressure in its second position of the first valve. Further, it relates to an adjustable second connection linked with the first chamber leading to the atmospheric pressure, whereby in case of the first chamber subjected to sufficient low pressure, the first membrane together with the second valve can be changed-over by a first position connecting the purge valve with atmospheric pressure into a second position connecting the purge valve with low pressure, and whereby the first valve in its second position releasing the first connection between the source of low pressure and the first chamber blocks the second connection leading to the first chamber and subjected to atmospheric pressure.
In order to keep waters pure, it is necessary that waste water reaches the clarification plants. Frequently this is not possible because of relatively high costs of conventional sewer systems or due to difficult local conditions like deficient natural downward gradient, small settlement density, unfavourable underground or crossing of a water protection zone. In addition, for such problems, it is possible to carry out disposal from clarification plant if low pressure drainage or “vacuum sewerage system” is used.
As essential components, appropriate vacuum sewerage system includes domestic shafts with a de-energized control system and stop valves or purge valves, a following line system with systematically arranged high and low points as well as a vacuum station with sewage collection tanks, sewage pumps, vacuum pumps, measuring and control technique. In order to convey waste water, this system flows from buildings via the usual free downward gradient building connection lines to a sump of a shaft laid within the plot, in which only pneumatically controlled stop valves and the associated control system are accommodated. Connected with the sump is an air-entrapped pitot tube, whereby the enclosed air is hydrostatically compressed by the liquid accumulated in the sump, so that a dynamic pressure is produced.
Thanks to the mechanism existing in the control system, the stop valve is opened in the presence of a fixed dynamic pressure and the waste water is exhausted into the vacuum line. Depending on time, the valve closes after a few seconds because of spring action and vacuum. The waste water is collected at the low points in the line system and is pushed by the added air gradually via the following high points toward the vacuum station. From the collection tank of the vacuum station the waste water is conveyed with the help of usual sewage pumps via a pressure pipe and a freefall chute to the clarification plant. In the collection tank and in the line system, a low pressure generator like a vacuum pump maintains a low pressure. The control system assigned to the stop valve should thereby facilitate an automatic matching to the waste water portions being which exhausted and to the operating conditions (e.g. the strength of the existing low pressure) in the drainage system.
A control system as per DE-C-43 36 020 is configured extremely compact and structurally simple and offers a high operating reliability. Regardless of the level of the available low pressure, a time control takes place essentially, which means that after the cessation of dynamic pressure, if the liquid is drawn off, then the control system closes the low pressure supply to the stop valve after a defined time interval and the stop valve is ventilated with ambient air, so that the stop valve is closed. The time interval remaining after purging before closing the purge valve serves for allowing transport air from the environment into the low pressure system. For system function, it would be desirable, if the volume ratio of let-in air and the absorbed liquid were higher, and weaker would be the prevailing low pressure. The above-mentioned control equipment is distinguished in particular by the fact that it keeps the after-opening time nearly constant for air and smaller the volume of exhausted waste water, the weaker would be the existing low pressure. A further advantage of this control equipment lies in effecting a suddenly changing condition of control to that extent that the connection to the second valve controlling the stop valve can be changed over all of a sudden.
Further, U.S. Pat. No. 4,373,838 discloses a control system as offered under the nomenclature “AIRVAC”. In order to facilitate a time control via a pressure-adjustable chamber, hoses with small diameter are necessary, which can be easily added, so that efficiency is not always guaranteed, especially when the supplied ambient air is dirty or damp. Even a clear On/Off-control of a valve, guiding the low pressure to the stop valve, is not specified. This means that it can come to a flutter of the stop valve with weak low pressure. In addition, the quantity of waste water and/or waste water air-mixture per opening cycle of the stop valve is not clearly defined. This can lead to malfunctions, in particular with large waste water accumulation. Further, it is disadvantageous that the suction time is dependent on low pressure existing in a system that is unfavourable for the entire system, since the opening times are dependent on the prevailing low pressure for their part. So the opening time in case of small low pressure is shorter than with strong low pressure. Thus, the danger exists with weak low pressure and large quantities of water collected in the sumps that the supply network is flooded and thus a normal function is no longer specified; for, with a flooded system the low pressure strength continues to decrease.
Further, it is unfavourable that the second valve releasing the low pressure to the stop valve can be opened with negligible low pressure, which is not always sufficient for rapid suction. Thereby, the danger arises that waste water is raised into the frost range of the line and can freeze out there.
DE-A-37 27 661 discloses a pneumatic control device for a stop valve at a low pressure sewer. In order to ensure a precision setting and reliable functioning of the control device, at least one control valve as well as a minimum low-pressure relief valve is necessary, besides a first valve actuated by a dynamic pressure and an elaborately designed time-control mechanism.
A control system of the type initially specified can be inferred from EP-A-1 091 053, which is simply set up and guarantees that liquid cannot penetrate into the chamber subjected to low pressure.
Further control systems for a purge valve that can be actuated by low pressure can be inferred from EP-A-0 649 946, DE-A-100 26 843, DE-U-296 16 003 or DE-B-10 2006 028 732.